1. Field of the Invention
The present invention relates to a high heat-resistant member including a graphite substrate having a surface covered with a carbide coating film, and a method for producing the same. The present invention also relates to a graphite crucible including the high heat-resistant member, and a method for producing a single crystal ingot using the graphite crucible.
2. Description of the Related Art
When a wafer of single crystal silicon carbide (SiC), gallium nitride (GaN) or the like is produced by sublimation (recrystallization) or other techniques, a seed crystal for single crystal and raw material powder (e.g., SiC powder) placed so as to face each other need to be heated at 2,000 to 2,400 deg. C. in an inert atmosphere. In this case, members capable of withstanding high temperatures are necessary and high heat-resistant members such as graphite heaters and graphite crucibles including (isotropic) graphite substrates have been used.
When a high heat-resistant member including an as-produced graphite substrate is used in a reducing atmosphere at high temperatures, the graphite substrate reacts with the reducing gas and decreases in weight, so durability of the high heat-resistant member decreases remarkably and there arises a risk that impurities are mixed in a product (single crystal).
In order to reduce these problems, the following patent literature and others proposed to shield the graphite substrate for protection from an external environment by covering a surface of the graphite substrate constituting a high heat-resistant member with a metal carbide (e.g. tantalum carbide) having a ultrahigh melting point.